diff --git a/packages/coding-agent/docs/extensions.md b/packages/coding-agent/docs/extensions.md
index cb02960f3..7038351d1 100644
--- a/packages/coding-agent/docs/extensions.md
+++ b/packages/coding-agent/docs/extensions.md
@@ -216,6 +216,12 @@ export default async function (pi: ExtensionAPI) {
 
 This pattern makes the fetched models available during normal startup and to `pi --list-models`.
 
+### Long-lived resources and shutdown
+
+Extension factories may run in invocations that never start a session. Do not start background resources such as processes, sockets, file watchers, or timers from the factory.
+
+Defer background resource startup until `session_start` or the command/tool/event that needs the resource. Register an idempotent `session_shutdown` handler to close any session-scoped resources you start.
+
 ### Extension Styles
 
 **Single file** - simplest, for small extensions:
@@ -471,7 +477,7 @@ pi.on("session_tree", async (event, ctx) => {
 
 #### session_shutdown
 
-Fired before an extension runtime is torn down.
+Fired before a started session runtime is torn down. Use this to clean up resources opened from `session_start` or other session-scoped hooks.
 
 ```typescript
 pi.on("session_shutdown", async (event, ctx) => {